Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency divisional multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals (e.g., user equipment (UE)), each of which can communicate with one or more base stations over downlink or uplink resources.
In addition, communication systems can include a multiple-input multiple-output (MIMO) system employing multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antenna layers may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. The MIMO system can provide improved performance (e.g., higher throughput, greater reliability, etc.) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized and radio conditions over each of the multiple antennas are desirable. Similarly, in some examples, communication systems can include a multiple-input single-output (MISO) system employing multiple (NT) transmit antenna layers to provide transmit diversity, and a single receive antenna layer.
In such systems that utilize multiple (NT) transmit antenna layers, a receiving entity (e.g., a UE) can select and indicate a rank to a transmitting entity (e.g., a network entity), where the rank specifies a number of antenna layers (which may relate to a number of physical or virtual antennas) to utilize in transmitting to the receiving entity. The receiving entity computes a sum of transport block sizes (TBS) estimated for each antenna layer corresponding to a given rank and compares the sums to determine a rank with the largest sum TBS. In estimating the TBS, the receiving entity estimates channel quality for each antenna layer with a given beamforming vector and converts the channel quality to a corresponding TBS. Estimating TBS in this regard, however, may not always lead to optimal rank selection.